Michael Mewhinney May 16, 1995
Ames Research Center, Mountain View, CA
(Phone: 415/604-3937)
RELEASE: 95-69
NASA TESTS NEW NOISE REDUCTION JET EXHAUST NOZZLE
NASA's Ames Research Center, Mountain View, CA, is
testing an advanced jet exhaust nozzle designed to reduce
noise produced by a 21st century High Speed Civil Transport
(HSCT) without adversely affecting the plane's takeoff
performance.
The tests are part of NASA's High Speed Research Program,
which is evaluating technologies needed for development of a
300-passenger supersonic transport that is both economically
practical and environmentally acceptable.
"The commercial success of the next-generation HSCT
depends upon its ability to satisfy mandated community noise
regulations governing aircraft operations," said project
manager Brian Smith, an Ames aerospace engineer.
As proposed, the HSCT would be capable of flying at Mach
2.4 (2.4 times the speed of sound) and have a range of 5,000
to 6,000 nautical miles. Envisioned to fly long distances
over water, the HSCT could reduce the Los Angeles to Tokyo
flight time from about 10 hours to only four. The expected
date for beginning service is 2006.
The High-Lift Engine Aeroacoustics Technology (HEAT)
tests are being conducted in Ames' 40-by-80-Foot Wind Tunnel
in cooperation with Boeing Commercial Airplane Group, Seattle,
WA; McDonnell Douglas Aerospace, Long Beach, CA; General
Electric Aircraft Engines, Cincinnati, OH; and Pratt &
Whitney, Hartford, CT. The 19 weeks of tests will continue
through May 26.
"These tests will provide critical information needed to
evaluate the suitability of ejector-type suppressor nozzles
for the HSCT," said Michael Dudley, assistant manager of Ames'
High Speed Research Office.
"There are three technical challenges to overcome in
order to build a supersonic transport," Smith said. "The
first is to make the HSCT quiet on takeoff and landing. We
want the HSCT to be at least as quiet as a conventional
subsonic jet transport."
The second challenge is to ensure that the sonic boom
created during supersonic flight does not adversely affect
people or wildlife. "As a result, when operating
supersonically, the HSCT will probably only fly over water or
land where the sonic boom is not detrimental to the
environment," Smith said.
The last challenge has aerospace engineers studying how
to reduce pollution produced by turbojet engines operating in
the stratosphere. During the HEAT tests at Ames, engineers
are concentrating on the first of these three challenges.
Working with NASA's Langley and Lewis Research Centers as
well as the aerospace industry, project engineers are testing
a mixer-ejector nozzle on a semi-span conceptual model of an
HSCT. Developed by General Electric, the exhaust nozzle is
designed to reduce the HSCT's noise during takeoff and landing
without adversely affecting its performance.
The semi-span, 13.5 percent scale model is comprised of a
wing and half-fuselage of a Boeing "Reference H" concept
supersonic transport. The model will be wind tunnel tested at
speeds of up to 300 knots (345 miles per hour).
"The Reference H model is the configuration being used
for a variety of HSCT studies by the High Speed Research
Program," Smith said. "It incorporates the latest aerodynamic
features that Boeing brings to the table and is representative
of current HSCT designs."
The 42-foot-long aircraft model is mounted on a four-foot
high sound-absorbing platform called a splitter plate. The
platform is insulated with ten inches of acoustic foam to
absorb noise generated by a propane-powered jet engine
simulator developed by Boeing and NASA.
A pair of microphones mounted on traversing struts beside
the platform and four microphones suspended from the wind
tunnel's ceiling enable engineers to measure jet noise at
different speeds, flap configurations and angles of attack.
The mixer-ejector nozzle is mounted on the trailing edge
of the model's semi-span wing. The nozzle has large air
intakes which act like giant vacuum cleaners. During the wind
tunnel tests, cool air flows over the model and through the
nozzle's air intakes, where it mixes with hot air from the jet
simulator.
"This cools the exhaust and reduces the velocity without
affecting the thrust," Smith said. "The net effect is that we
can maintain the same thrust while reducing the jet's velocity
and hence the jet noise when the aircraft is taking off with
300 passengers," Smith said.
"HEAT is the first test to accurately measure the effects
this nozzle has on the noise and performance of the aircraft,"
Smith said. "This is important from an environmental
standpoint, because if the nozzle causes the aircraft to
develop less lift, the only way to compensate is to take off
at a higher angle," Smith said. "That requires more thrust
and more thrust means more noise," he added.
"What we want is an efficient airplane that can take off
at a low angle of attack with high ratios of lift to drag,"
Smith said. "Low drag means less thrust, and less thrust
means less noise."
-end-
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